1. Field of the Invention
This invention relates to a dropout compensating apparatus used for a video signal recording/reproducing apparatus such as a video tape recorder and a video disc player, for compensating a dropout contained in a video signal reproduced from a recording medium.
2. Description of the Prior Art
Recently, the video signal recording/reproducing apparatus such as video tape recorders (VTR) and video disc players have been provided with a dropout compensating unit which substitute a reproduced video signal having a dropout portion with a signal one horizontal (1 H) scanning period before by using the line correlation of television (TV) picture. FIG. 1 shows a block diagram of the dropout compensating unit which has been widely used. A frequency modulated (FM) video signal reproduced from a reproducing head is fed to an input terminal 1, and, when contains no dropout portion, is passed through an input terminal of an electronic switch 2, the electronic switch 2, and the output terminal 9 of the electronic switch 2 to a demodulator 5. When the reproduced FM video signal contains a dropout portion, a dropout detector 3 detects the dropout and controls the switch 2 to connect another input terminal 8 of the switch 2 to the output terminal 9. The input terminal 8 is applied with an output signal of an one horizontal period (1 H) delay line 4 which delays the signal from the output terminal 9 by 1 H. Thus the reproduced FM video signal containing a dropout portion is not applied to the demodulator 5, but instead, the 1 H previously reproduced FM video signal is applied to the demodulator 5. Accordingly, the demodulator 5 is always applied with FM video signals containing no dropout portions and demodulates and outputs the same at an output terminal 6.
However, the 1 H delay line is an analog delay line usually composed of a glass delay line, which is difficult to be small-sized. Further, when the dropout portion occupies the period longer than 1 H, the same video signal must be repeatedly circulated the loop composed of the switch 2 and the 1 H delay line 4 so that it is degraded (reduced in amplitude and bandwidth) due to the nonlinearity and insertion loss of the 1 H delay line 4.